Dr David Holwell (University of Leicester)
Dr Iain McDonald (Cardiff University), Dr Hannah Hughes (Camborne School of Mines, University of Exeter), Prof Gawen Jenkin (UoL), Andy Lloyd (Anglo American), Fiona Stevens (Anglo American).
The Northern Limb of the Bushveld Complex, South Africa is host to the world’s largest resource of platinum-group elements (PGE), along with significant nickel, copper and cobalt in a complex magmatic sulfide ore deposit. All of these resources are linked with environmentally-friendly technologies and energy usages in the automotive industry, with the PGE being essential components in catalytic converters, and Ni, Co and Cu critical metals in Electric Vehicle batteries. As such, the northern limb of the Bushveld is likely going to play a large part in the switch to cleaner automotive technology.
The major deposit in the Critical Zone of the northern Bushveld (commonly known as the ‘Platreef’) rests directly on variable basement of Archaean and Paleoproterozoic units at surface. Down dip, it overlies Bushveld Complex Lower Zone rocks; themselves prospective for base metal sulfide mineralisation. The stratigraphy, structure, mineralization styles and metal budgets of the Northern Limb of the Bushveld Complex show important differences to the other limbs of the complex. The underlying causes behind these differences are poorly understood and no geological model exists to investigate them on anything more than a local scale.
This PhD project aims to tackle questions surrounding the controls on the metal distribution through the Critical Zone; processes that occur after emplacement during cooling and crystallisation but are fundamental in determining the metallurgical characteristics of the ores. The project is in partnership with Anglo American, who have been mining the Platreef via surface methods since the 1990s, and now operate the world’s largest PGE surface mining operation at the Mogalakwena Mine. Whilst the near-surface resources are reasonably well characterised, the down dip potential and extension of resources is known, but has had no research work completed on it thus far. Therefore, this PhD provides the opportunity to work on one of the world’s greatest ore deposits, with resources critical for a greener future, and at a time when exploration and mining activities in the area are expanding.
1. Can Critical Zone mineralisation (in terms of metal tenors, ratios and host lithologies) be correlated from the shallow, Platreef resources into the deeper Platreef, and does it extend into predictable stratigraphic units of the Critical Zone?
2. Why are some zones more PGE-rich and others more base metal-rich?
3. How does fluid interaction affect metal ratios and sulphide tenors? How does alteration affect the metallurgical characteristics of the ores?
4. How do the metallurgical characteristics affect the amenability to processing using conventional and novel approaches?
In order to tackle the research questions, a multi-disciplinary approach will be used whereby the PhD researcher will undertake fieldwork in South Africa and make use of an unrivalled collective resource of laboratory facilities at Leicester, Cardiff and CSM (Exeter).
A. Fieldwork in South Africa to sample extensive drill core of the shallow and deeper stratigraphy of the northern Bushveld Complex. This will include basement, Lower Zone, Lower and Upper Critical Zone, and the base of the Main Zone units. Sampling from drillcore will form the basis of lab work to tackle questions 1-4 (see B-E).
B. Detailed and careful stratigraphic correlations in terms of mineralogy (including the use of hyperspectral data) and chalcophile metal geochemistry between boreholes to address questions 1 and 2.
C. Textural and quantitative mineralogy; platinum-group mineral studies; bulk chalcophile geochemical characteristics; to address question 3. Automated mineralogy will also determine metal deportment and grain association – thus giving early insight on processing amenability relevant to question 4.
D. In situ leaching experiments of PGE-bearing minerals and base metal sulfides using novel deep eutectic solvent processing to address question 4.
In terms of the scientific developments in understanding the Northern Limb specifically, and the genesis of such ore deposits more generally, the project will assess the degree of correlation between ‘normal’ Upper Critical Zone stratigraphy and mineralisation with the Northern Limb; test the multi-sill emplacement model and assess the effects of contamination; and identify and assess the importance of fluid interaction during emplacement.
The application of this to industry includes an improved understanding the predictability of grade along strike and downdip; and help to understand and predict the geometallurgical characteristics of the ore along strike and down dip, as controlled by varying degrees of magmatic versus hydrothermal processes. The deep eutectic solvents can potentially be an effective, high-recovery method of processing that vastly reduces energy and water usage and is therefore an environmentally friendly alternative to some conventional processing techniques. This project will help to assess how applicable this novel technology is to these PGE-base metal ores.
This PhD forms part of a large consortium project (NL4D) funded by Anglo American involving Leicester, Cardiff and CSM. The project runs for five years from January 2020 and will include three PhD studentships (two based at Leicester) working alongside senior researchers, postdocs and Masters students from all three universities. The PhD researcher will have access to labs at all three institutions and the opportunity to spend some extended period working at each. There will be regular interaction with Anglo American through fieldwork, internal reporting and workshops/meetings in South Africa and the UK. The PhD researcher will be encourage to present their results at national and international conferences each year, including the International Platinum Symposium in 2022 and the Biennial meetings of the SGA (e.g. Rotarua, New Zealand, 2021).
Grobler, DF, Brits, JAN, Maier, WD and Crossingham, A., 2018, Litho- and chemostratigraphy of the Flatreef PGE deposit, northern Bushveld Complex. Mineralium Deposita 54, 3-28.
Holwell DA, Adeyemi Z. Ward LA, Smith DJ, Graham SD, McDonald I, Smith JW. 2017. Low temperature alteration of magmatic Ni-Cu-PGE sulfides as a source for hydrothermal Ni and PGE ores: a quantitative approach using automated mineralogy. Ore Geology Reviews, 91, 718-740
Klemd, R., Herderich, T., Junge, M., Oberthur, T., Schouwstra, R., Roberts, J. 2016. Platinum-group element concentrations in base-metal sulphides from the Platreef, Mogalakwena Platinum Mine, Bushveld Complex, South Africa. Journal of South African Geology, 119, 623-638.
McDonald I, Holwell DA. 2011. Geology of the Northern Bushveld Complex and the Setting and Genesis of the Platreef Ni-Cu-PGE Deposit. Reviews in Economic Geology 17, 297-327.